Export observable.dart to avoid linter issues in apps importing objectbox

Author: vaind

CHANGELOG.md

@@ -2,7 +2,9 @@
 
 * Change `box.get(id)` to return null instead of throwing when trying to read a non-existent object.
 * Add "empty" query support using `box.query()`.
-    (thanks [@Buggaboo](https://github.com/Buggaboo) for [#132](https://github.com/objectbox/objectbox-dart/pull/132))     
+    (thanks [@Buggaboo](https://github.com/Buggaboo) for [#132](https://github.com/objectbox/objectbox-dart/pull/132))
+* Expose `lib/observable.dart` to avoid linter isues in apps using objectbox.
+    (thanks [@cmengler](https://github.com/cmengler) for bringing this up in [#141](https://github.com/objectbox/objectbox-dart/pull/141))    
 * Documentation and examples updates & improvements.
 
 ## 0.8.0 (2020-10-13)

README.md

@@ -164,7 +164,7 @@ Streams can be created from queries.
 Note: Dart Streams can be extended with [rxdart](https://github.com/ReactiveX/rxdart).
 
 ```dart
-    import "package:objectbox/src/observable.dart";
+    import "package:objectbox/observable.dart";
 
     // final store = ...
     final query = box.query(condition).build();

example/flutter/objectbox_demo/lib/main.dart

@@ -3,7 +3,7 @@ import 'package:objectbox/objectbox.dart';
 import 'package:intl/intl.dart';
 import 'package:path_provider/path_provider.dart';
 import 'objectbox.g.dart';
-import 'package:objectbox/src/observable.dart';
+import 'package:objectbox/observable.dart';
 import 'dart:async';
 import 'dart:io';
 

lib/observable.dart

@@ -0,0 +1 @@
+export 'src/observable.dart';

test/stream_test.dart

@@ -1,6 +1,6 @@
 import 'dart:async';
 
-import 'package:objectbox/src/observable.dart';
+import 'package:objectbox/observable.dart';
 import 'package:test/test.dart';
 
 import 'entity.dart';